Molding sand, also known as foundry sand, is a

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

that when moistened and compressed or

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

ed or heated tends to pack well and hold its shape. It is used in the process of

sand casting Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced i ...

for preparing the mold cavity.

Green sand

Green sand is an aggregate of sand,

bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay parti ...

pulverized coal Coal dust is a fine powdered form of which is created by the crushing, grinding, or pulverizing of coal. Because of the brittle nature of coal, coal dust can be created during mining, transportation, or by mechanically handling coal. It is a form ...

and

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

. Its principal use is in making molds for

metal casting In metalworking and jewelry making, casting is a process in which a liquid metal is delivered into a mold (usually by a crucible) that contains a negative impression (i.e., a three-dimensional negative image) of the intended shape. The metal is ...

. The largest portion of the aggregate is a sand, either most-commonly silica or sometimes

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

. There are many recipes for the proportion of clay, but they all strike different balances between moldability, surface finish, and ability of the hot molten metal to degas. The coal, typically referred to in as sea-coal, which is present at a ratio of less than 5%, partially combusts in the surface of the molten metal leading to offgassing of organic vapors. Sand casting is one of the earliest forms of casting practiced due to the simplicity of materials involved. It still remains one of the cheapest ways to cast metals because of that same simplicity. Other methods of casting, such as those using shell molds, boast higher quality of surface finish, but have higher cost. Green sand (like other casting sands) is usually housed in what foundry workers refer to as "

flask Flask may refer to: Container * Hip flask, a small container used to carry a small amount of liquid * Laboratory flask, laboratory glassware for holding larger volumes than simple test tubes ** Erlenmeyer flask, a common laboratory flask with ...

", which are nothing other than boxes without a bottom or lid. The box is split into two halves which are stacked together in use. The halves are referred to as the cope and drag flask respectively. Born bronze - Bronze casts

Not all Green sand is green in color. But considered "green" as in the sense that it is used in a wet state (akin to green wood). According to the Cast Metals Federation website, an alternative casting method is to heat-dry the molded sand before pouring the molten metal. This dry sand casting process results in a more rigid mold better suited to heavier castings.

History

There is no clear record in history to attribute the first metal casting and use of molding sand, but ancient artifacts and writings allude to a period around 3200 B.C. in ancient Mesopotamia. The history of molding sand is difficult to study, as much of the origins of the practice predate writing. Molding sand was used exclusively for bronze casts, which was pioneered by the ancient Chinese. The next major advancement came in India in 500 B.C. when cast-crucible steel was created. Eventually, Sir

Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for the ...

first did aluminum castings in Great Britain, around 1808. In modern times, the United States produces 8.4 million tons of iron castings, 1.4 million tons of steel castings, 1.7 million tons of aluminum castings, and 321 thousand tons of copper castings annually. Much of the modern metal industry has innovated because of a massive increase in sand quality due to better instrumentation, as well as metallurgy, and better understanding of metal properties.

References

{{Metalworking navbox, castopen Casting (manufacturing) Sand

Green sand

See also

History

References